Friday, July 7, 2017

LIGO data whitening is exposed

Elliot McGucken alerts me to LIGO controversies.

Peter Woit debunks claims that LIGO confirms the extra dimensions of string theory. I have previously complained that LIGO uses fake data injections, with only 3 ppl knowing whether a black hole collision has been faked.

Quanta mag reports:
Wave Observatory (LIGO) announced that they had successfully detected gravitational waves, subtle ripples in the fabric of space-time that had been stirred up by the collision of two black holes. The team held a press conference in Washington to announce the landmark findings.

They also released their data.

Now a team of independent physicists has sifted through this data, only to find what they describe as strange correlations that shouldn’t be there. The team, led by Andrew Jackson, a physicist at the Niels Bohr Institute in Copenhagen, claims that the troublesome signal could be significant enough to call the entire discovery into question. The potential effects of the unexplained correlations “could range from a minor modification of the extracted wave form to a total rejection of LIGO’s claimed [gravitational wave] discovery,” wrote Jackson in an email to Quanta. LIGO representatives say there may well be some unexplained correlations, but that they should not affect the team’s conclusions. ...

For now, confidence is high in LIGO’s conclusions. “The only persons qualified to analyze this paper are in the LIGO Scientific Collaboration,” said Robert Wagoner, a theoretical physicist at Stanford University who is not affiliated with LIGO. “They are the only ones who have had access to the raw data.” Steinn SigurĂ°sson, an astrophysicist at Pennsylvania State University who is also not affiliated with either team, agrees. “For now, I’d definitely go with the LIGO people,” he said. “It is very rare for outsiders to find major errors in a large collaboration.”

Nevertheless, “it’s going to take longer than people would like” to get these issues resolved, said SigurĂ°sson. “It’s going to take months.”
This is funny. Did LIGO release its data or not? If LIGO released its raw data, then others have access to it.

A lot of researchers do not release their raw data, and thus avoid the detailed scrutiny of others. Their attitude is often that competing researchers should go do their own experiments, and collect their own data.

The London Daily Mail explains:
The ensure the results are accurate, LIGO uses two observatories, 3,000 kilometers apart, which operate synchronously, each double-checking the other's observations.

The noise at each detector should be completely uncorrelated, meaning a noise like a stormnearby one detector doesn't show up as noise in the other.

Some of the sources of 'noise' the team say they contend with include: 'a constant 'hiss' from photons arriving like raindrops at our light detectors; rumbles from seismic noise like earthquakes and the oceans pounding on the Earth's crust; strong winds shaking the buildings enough to affect our detectors.'

However, if a gravitational wave is found, it should create a similar signal in both instruments nearly simultaneously.

The main claim of Jackson's team is that there appears to be correlated noise in the detectors at the time of the gravitational-wave signal.
The main idea behind LIGO is to have two detectors, 2000 miles apart, and look for correlations in the data. Each detector by itself just looks like noise. Any big correlation is assumed to be a black hole collision in a distant galaxy.

Finding correlations should be child's play, but it takes the LIGO team many months to announce that they found a correlation.

Here is the LIGO response:
LIGO analyses use whitened data when searching for compact binary mergers such as GW150914. When repeating the analysis of Creswell et al. on whitened data these effects are completely absent. 3. Our 5-sigma significance comes from a procedure of repeatedly time-shifting the data, which is not invalidated if correlations of the type described in Creswell et al. are present.
In other words, the LIGO team massages the data to get rid of the small correlations found by the critics.

This is lame. It is appears that the LIGO team is whitewashing some data in order to make their black hole collision model appears more accurate. They do not want to admit that there are some unexplained correlations.

LIGO Skeptic blog is also all over this.


  1. Yes!

    Did they or did they not release the data?

    Did they or did they not release the correct methods for analyzing the data?

    Why would they release fake data or manipulated data? Would that not be harder?

    And why wouldn't they share the full details of how they analyzed the data? What would be the use of folks analyzing data in the wrong or non-optimum manner?

    Not looking very good for LIGO at this point. Especially after the way they overhyped the signal complete with sound effects and "chirping" for the public's consumption. Perhaps the true sound was more like farting or burpring, rather than chipring?

  2. Here's the solid response to the lame LIGO response:

    They conclude:

    "It would appear that the 7 ms time delay associated with the GW150914 signal is also an intrinsic property of the noise. The purpose in having two independent detectors is precisely to ensure that, after sufficient cleaning, the only genuine correlations between them will be due to gravitational wave effects. The results presented here suggest this level of cleaning has not yet been obtained and that the identification of the GW events needs to be re-evaluated with a more careful consideration of noise properties."